Twotter Load and Trim sheet

[Rudeman]

Dear all,
We are in serious need of a Twotter load and trim sheet. Either electronic or very good copy to print some books.
The current one we have is about 10th generation.
Any guidance will be appreciated, will swap for beers !!!

[V1... Ooops]

Speak to your aircraft engineer - ask him (or her) to have a look inside the aircraft weight and balance documentation book that they have in their maintenance library. You will probably find a first generation (original) blank loadsheet in there that you can photocopy.

Michael

[V1... Ooops]

Since I posted the reply above, quite a few friends and former students have emailed me and asked for additional information. Instead of trying to send everyone an email from my (rather slow) dial-up connection in East Africa, I am going to post the information here in JPEG format - so, you can right-click on the images and chose "save picture as...", and now you have them.

The images below were taken from Chapter 18 of the FlightSafety Twin Otter Pilot Training Manual, revision 2, February 1996. When I wrote this manual, I simply took the entire contents of the first half of the Twin Otter Weight and Balance Handbook (PSM 1-63-2) and reproduced this information in the Pilot Training Manual. de Havilland never claimed a copyright on this information (heck, they wanted it to be widely disseminated and reproduced), for that reason, I have no concerns about reproducing it here. There are three images below. The first shows the arms for various locations through the aircraft, the second provides this same information in graphic form, and the third is an example of one way to make up a fairly simple loadsheet. Neither I nor DHC are suggesting that you have to do it this way - but, this way has been proven to work, and all you need to make it work is a pencil and a calculator.

The complete version of what you see below (about 20 pages altogether) can be found in the Weight and Balance Handbook that your aircraft engineers have in their technical library.

Regards, Michael

Table of Arms (300 series)
http://www.hostdub.com/albums/PanEuropean/Arm_Table.jpg

Graphical Depiction
http://www.hostdub.com/albums/PanEuropean/Seat_arm.jpg

Sample Loading Manifest
http://www.hostdub.com/albums/PanEuropean/Manifest.jpg

Be aware that the riskiest configuration for a Twin Otter, so far as balance is concerned, is with two pilots, no cargo or pax, and very little fuel on board (e.g. 200 pounds each tank). Do a sample calculation for your aircraft in this configuration and see what the result is. If you have a heavy load of old avionics in the nose, you might just find that you are outside of the forward CG limit.

If you find that your aircraft is within the CG limit under the circumstance described in the paragraph above, then the suggestion below (a note I sent out to one person earlier this week) might provide some helpful guidelines for you when it comes to planning the seat assignments for your self-loading cargo.

A post-script for you that might help quite a bit - for almost all DHC-6 aircraft that do not have very, very elaborate and heavy avionics installations in the nose (just aft of the nose baggage compartment, or just forward of station 60), the following practical loading strategy will ALWAYS yield an aircraft that is within C of G limits at both landing and takeoff, assuming that the fuel load is reasonably balanced:

1) Put two pilots and their kit in the two pilot seats, assume a maximum weight of 400 pounds for all that.

2) Split the baggage compartment loads equally between the nose and the rear compartment until the nose compartment reaches its limit (typically about 275 pounds if you have radar installed, 300 pounds if no radar), then put the rest of the load in the rear compartment.

3) Assume normal human behaviour of the passengers as follows:

a) they will occupy all the window seats first, before they begin to sit three abreast.

b) they will distribute themselves evenly forward and aft of row 3/4

If these conditions exist, then the aircraft will almost always, always be properly balanced for both takeoff and landing. It is not necessary to compensate for the slight imbalance in fuel load due to the different capacity of the forward and aft fuel tank. Note that the difference in CG as the fuel burns down from full tanks to zero fuel is almost too small to measure - it is less than the effect of one standard weight passenger changing seats from row 4 to row 3.

Note that if you happen to be carrying morbidly obese passengers (e.g. Americans), don\'t let these obese passengers sit in row 7 - the row against the aft bulkhead of the passenger cabin. Put them in rows 3, 4, or 5. FYI, the balance point of the plane (the C of G of the plane) will almost always be between rows 3 and 4, assuming standard seat fitment.

If you really want to fine-tune things, try to load so you are closer to your aft CG limit than to your forward CG limit. You get better fuel economy with an aft CG, and you also minimize the risk of damage to the nosewheel on unimproved surfaces, especially during the landing flare.

Lastly - this is very important for your safety - make a very close inspection of the forward edge of the elevator where it meets the horizontal stabilizer, and make sure that you have wiper seals installed on the forward edge of the elevator. If these wiper seals are missing - and this seems to be a common problem with South African registered (translation = South African painted and South African maintained) aircraft, then you lose an enormous amount of elevator authority at low speeds (approach), and this is a far more dangerous situation than an improperly loaded aircraft. In fact - you will not be able to keep the nose up during the flare with full flap if your CG is at all towards the forward end of the CG limit. The Twin Otter maintenance manual provides full details of the location of the wiper seals, and the allowable gap (which is quite small - about ten thou of an inch).

- - - - - - - -

Below is a picture of a Twin Otter that I found with wiper seals missing - now you know where to go looking for them. They are critically imporant for low speed handling - most especially the final stages of approach. If the wiper seals are missing, you will lose elevator authority just when you need it the most - in the flare, when you are making a full flap landing. You also lose the ability to keep the nosewheel up off the runway at low airspeeds.

See the maintenance manual for exact instructions about where they should be, how to install and trim them, and how to re-balance (statically) the elevator control surface after they have been installed.

Michael

Twin Otter Elevator-Horizontal Stabilizer with missing wiper seal
http://www.hostdub.com/albums/PanEuropean/Missing_Wiper_Seal.jpg

[Shrike200]

That was almost too comprehensive - back off man, you're giving us an inferiority complex!

The photo of the missing seals - no, no, no. Thats just too professional.

But seriously - isn't there the print of the 'step this way then that' mass and balance sheet?

[mventre]

I'm one of Mike's former students. He taught me how to fly this bucket of bolts almost 10 years ago. Thanks to Mike's extensive experience on the DHC6 it was one of the best courses I've taken. I highly recommend it to anyone operating the Twin Otter.

Kudos to the depth of knowledge and professionalism of people like Mike.

P.S. Here's the missing sheet I think people are looking for.

Regards,

A Different Mike

http://home.earthlink.net/~mwventre/sitebuildercontent/sitebuilderpictures/dhc6.jpg